1. Field of the Invention
The present invention relates in general to a repair circuit for a redundancy circuit for performing a repair operation to replace a failed circuit with the redundancy circuit in a manufacturing process of a memory device, and more particularly to a repair circuit for a redundancy circuit which uses an anti-fuse rather than a conventional fuse, to perform a repair operation at a package step of the memory device.
2. Discussion of the Related Art
Generally, a memory device such as a dynamic random access memory (DRAM) device comprises a large number of minute memory cells and cannot perform its function when any one of the memory cells fails. In this case, the DRAM device is regarded as an inferior article to be discarded. Meanwhile, the integration degree of a DRAM device is on an increasing trend and only a smaller number of memory cells therein thus have a high probability of failing. However, the discarding of a failed DRAM device is inefficient in that doing so reduces yield. In order to increase the yield, a redundancy circuit is preliminarily arranged in a DRAM device in such a manner that a failed memory cell can be replaced with a redundancy memory cell therein. The arrangement of such a redundancy circuit may cause problems such as an increase in chip area and an increase in the number of failure repairing tests. However, the redundancy circuit has been adopted by DRAM devices, actively beginning with 64K-256K devices, because such use results in little increase in DRAM chip areas DRAMS.
The redundancy circuit is arranged correspondingly to each sub-array block and has spare row and column stages which are driven to replace a failed memory cell with a redundancy memory cell. If a wafer process is completed, failed memory cells are detected through a testing process and the associated addresses are replaced with addresses of spare memory cells. At this time, an internal circuit is adapted to perform a programming operation of replacing the addresses of the failed memory cells with those of the spare memory cells. In practice, upon receiving an address corresponding to a failed line, the internal circuit replaces the failed line with a spare line. In order to perform the programming operation, there have been proposed various methods, for example, an electrical fuse method of applying an overcurrent to a fuse to open the fuse by melting, a laser cutting method of applying a laser beam to a fuse to open the fuse by burning, a method of interconnecting junctions using a laser beam, and a method of storing an associated program in an erasable programmable read only memory (EPROM). Among the above methods, the laser cutting method is widely used because it is simple, reliable and easy to lay out. In this case, the fuse is made of a polysilicon wire or metal wire.
FIG. 1 is a circuit diagram showing the construction of a conventional repair circuit which repairs a failed circuit using a general fuse.
With reference to FIG. 1, an operation switching part 10' is adapted to precharge the entire circuit with a source voltage VCC in response to a complementary precharge signal prechb. A sense signal input part 20' is connected between the operation switching part 10' and ground through a fuse PF. The sense signal input part 20' is turned on in response to an address signal ADDR of a failed circuit to sense a blown state of the fuse PF. An output part 30' is adapted to output a voltage value at a common connection point of the operation switching part 10' and one side of the fuse PF. A latch part 80' is adapted to stabilize an output value from the output part 30' when the fuse PF is programmed.
The operation of the conventional repair circuit with the above-mentioned construction will hereinafter be described briefly.
If the complementary precharge signal prechb becomes low in level at a normal state, the operation switching part 10' is turned on to apply the source voltage VCC to the fuse PF. Upon inputting the address signal ADDR under this precharged condition, the sense signal input part 20' is turned on, resulting in the forming of a current path where current of the source voltage VCC from the operation switching part 10' flows to ground through the fuse PF and sense signal input part 20'. As a result, the voltage across the fuse PF becomes low in level. This low level voltage is inverted by an inverter in the output part 30', thus making a complementary repair value repb high in level at the normal state.
When the fuse PF (for example, a polysilicon fuse) is cut by a laser beam under the above condition, the current path, previously formed from the operation switching part 10' to ground through the fuse PF and sense signal input part 20', is blocked to make the voltage at one terminal of the fuse PF high in level. This high level voltage is inverted by the inverter in the output part 30', thus making the complementary repair value repb low in level. This complementary repair value repb is fed back to the latch part 80' to turn on a PMOS transistor therein. As a result, the source voltage VCC is transferred to the output part 30', so that the output value therefrom can be maintained stably even if the complementary precharge signal prechb is not input.
The complementary repair value repb is applied to replace a failed circuit with a redundancy circuit to effect a normal operation.
On the other hand, among the above-mentioned methods, the overcurrent cutting method requires a high current driver and fuse-blowing pad, resulting in an increase in occupying area. Further, in the case of cutting polysilicon using a laser beam, an error may occur in accurately applying the laser beam to the polysilicon and a residue may be present after the cutting. In this case, the laser cutting method requires a large amount of processing time and is inaccurate and difficult to perform. Further, the repair is impossible at a package level, resulting in a degradation in reliability.
In order to solve the above problems, there has recently been proposed a new element, or a so-called anti-fuse, which can be programmed simply even at the package level.
The anti-fuse is programmed to interconnect an upper electrode and lower electrode. Namely, the anti-fuse includes an insulating film formed between the upper and lower electrodes in such a manner that the film can easily be broken down according to a dielectric breakdown voltage, which is a voltage difference between the upper and lower electrodes.
In this regard, the anti-fuse is programmed to interconnect the two electrodes, whereas a general fuse is programmed to disconnect the electrodes from each other.
As a result, there is a need for a circuit which is capable of programming the anti-fuse and verifying the programmed result of the anti-fuse.